Dumbbell



FIG. 1 is a perspective view of the dumbbell showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a left-hand end view thereof; and

FIG. 6 is a right-hand end view of the dumbbell. 

The ornamental design for a dumbbell as shown. 